1. Field of the Invention
The disclosure relates to an image formation apparatus, and is preferably applied to an image formation apparatus of what is called a tandem system in which image formation units are disposed side by side in series in a conveyance direction of recording paper, for example.
2. Description of Related Art
Conventionally, some image formation apparatuses form a color image in such a way that image formation units of respective colors transfer images of the respective colors in a superimposed manner onto recording paper on a conveyance belt while the recording paper is conveyed successively to the image formation units of the respective colors. Some of such image formation apparatuses are configured to correct image formation conditions upon the occurrence of an event where the print density may vary, such as an event where a predetermined number of sheets of recording paper are to be printed. The images are thus stably formed by correcting the density of the images to be formed (for example, refer to Japanese Laid-open Patent Publication No. 2011-197417).
In the density correction, the image formation apparatus performs a calibration that involves: irradiating the conveyance belt with irradiation light; sensing the reflection light reflected from the conveyance belt; and adjusting the intensity of the irradiation light such that the light quantity of the reflection light can become a preset value. Then, the image formation apparatus prints a patch pattern for density correction on the conveyance belt, irradiates the patch pattern with irradiation light to sense the reflection light, detects the density of the patch pattern, and corrects the image formation conditions on the basis of the density. Such density correction is performed on the precondition that light reflection characteristics on the surface of the conveyance belt are almost uniform at any part in the conveyance belt.